This invention relates to electric machines and more particularly to improvements in the circulation of cooling gas through the structure of such machines.
Improvements in the efficiency of cooling rotating electrical machinery result in increased capacity or power output for a given machine. In machines which are cooled by the circulation of air or other gases, the coolant is generally forced through various passages in the machine by a fan. Attempts to improve cooling efficiency by maximizing the exposure of machine components to coolant and minimizing obstructions to the flow of coolant have resulted in machine designs which include coolant passages throughout the rotor and stator. Examples of such machines can be found in U.S. Pat. No. 2,724,064, issued Nov. 15, 1955; U.S. Pat. No. 3,660,702, issued May 2, 1972; and U.S. Pat. No. 3,684,906, issued Aug. 15, 1972.
In certain applications for electric machines such as alternators for vehicular auxiliary power systems, space and efficiency requirements sometimes do not allow the use of conventional fans for the circulation of coolant through the alternator. For these applications, electrical machines have been designed which circulate coolant through axial passages in the rotor and use the principle of centrifugal force to pump the coolant radially throughout the machine. U.S. Pat. No. 3,471,727, issued Oct. 7, 1969, discloses a machine which incorporates this type of cooling arrangement.
Machines which utilize salient pole rotors have been provided with wedges in the interpole spaces to conduct coolant through these spaces. U.S. Pat. No. 2,899,573, issued Aug. 11, 1959 discloses a salient pole rotor cooling wedge. The present invention utilizes cooling wedges with integral vanes and impeller elements in combination with multiple cooling passages and shrouds which prevent recirculation of coolant to provide for the efficient circulation of coolant throughout an electrical machine with a salient pole rotor.
An electrical machine, such as an alternator, constructed in accordance with the present invention includes a frame assembly with multiple inlet and outlet ports for the passage of a coolant such as air. A rotor within the frame assembly is provided with A-shaped wedges within each interpole space. These wedges include a vane and impeller on each end to force cooling air through the machine. Air entering through certain ports in the frame assembly passes through an exciter generator which is located at the drive end of the frame assembly. Air entering through other ports in the frame assembly passes through a rotating rectifier assembly located within the rotor.
After passing through the exciter generator and/or the rotating rectifier assembly, this air enters the main cooling circuit of the machne which comprises frame intake and exhaust ports, A-shaped wedges located within interpole spaces in the rotor, radial vanes and impellers on the ends of these wedges, shrouds on the ends of the wedges to prevent recirculation of cooling air, a gap between the stator assembly and rotor, and axial cooling passages in the stator assembly and frame.
Each of the A-shaped wedges include an axial rotor cooling passage which runs the length of the rotor. As the rotor turns, vanes on the ends of the wedges impart an outward flow due to centrifugal force action upon the air. Part of the air enters the slots in the wedges at the anti-drive end of the rotor. A portion of that air is expelled at the center of the rotor through holes in the center of the wedges while the remainder is expelled at the drive end of the rotor.
Air entering near both ends of the rotor is forced by the impellers, past the stator end turns and out one of the exhaust ports. Prior to being exhausted, air from the drive end of the stator passes through cooling passages in the frame.
Additional cooling paths are provided by a gap between the rotor and stator and by axial stator cooling passages in the stator assembly. These passages receive the air which had been expelled from the A-shaped wedges at the center of the rotor. This air is expelled through apertures in the wedges. Some of these apertures are radially aligned with openings in the axial stator cooling passages. This provides for the efficient transfer of coolant from the rotor to the stator assembly.
Shrouds on the end of the A-shaped wedges form close seals with the frame and the exciter generator to prevent recirculation of coolant after it has passed the impeller tabs. This ensures generally radial flow of coolant near each end of the rotor.